The commercial feasibility of processes for the preparation of medicinally valuable steroids depends, in the main, upon the availability and the cost of the starting materials. For example, in the synthesis of 19-norsteroids 3 described in U.S. Pat. No. 3,692,803, issued Sept. 9, 1972, ##SPC1##
The commercial viability of the process depends upon the cost and availability of the bicyclic unsaturated ketone 1 and the ethylenedioxy-beta-ketoester 2, the starting materials. A process for the preparation of 6,6-methylenedioxyheptan-2-one 5, the precursor of the beta-ketoester 2, ##SPC2##
Was disclosed in U.S. Pat. No. 3,767,677, issued Oct. 23, 1973. This process involved the ketalization of one of the two symmetrically situated keto groups of 4, and even though it was unexpectedly found that selective ketalization occurred in the presence of excess alkylene glycol, a minor amount of the diketal 6 was formed, in addition to the desired predominant monoketal 5. The formation of the diketal 6 necessitated a costly, inefficient and inconvenient separation step involving the formation of the bisulfite addition product of the monoketal 5, separation of the minor diketal 6 by extraction, hydrolysis of the bisulfite addition product to the major monoketal 5, hydrolysis of the diketal 6 to the dione 4 and recyclization of the dione 4 through the ketalization process. The economics of the process for the preparation of 7,7-ethylenedioxy-2-oxo octanoic acid ethyl ester 2 would be substantially improved and the availability of these steroid starting materials would be materially increased if a process for the preparation of the monoketal 5, eliminating the costly, inefficient and inconvenient bisulfite separation and recyclization steps of the process described in the aforementioned patent was available. The present invention describes a process which avoids the bisulfite separation and recyclization steps.